AUSTIN - Two office towers that will add almost 1 million sf to downtown Austin are set to begin construction in the coming months.

The 32-story office portion of Trammell Crow’s Block 23 Green Water Treatment Plant redevelopment project is expected to begin construction in April 2015, with completion scheduled for November 2016.

The apartment tower portion of the mixed-use project has been under construction for several months.

The $100 million project is on Cesar Chavez St. between San Antonio St. and Lamar St., in one of the most intensive development sites in the country. It is expected to add 492,333 sf of office and 6,806 sf of retail to the area.

Schlosser Development Corp. is also preparing to build a $52 million, two-building office project on a 2.7-acre site at 835 W. Sixth St. Shoal Creek Walk is expected to have 430,417 sf of office space and 44,427 sf for retail.

The Schlosser website indicates the project will include 17 floors of office — one building of 12 stories and one building of five stories — and ground level retail.

The push to develop more offices downtown probably has been encouraged and expedited by the success that Cousins Properties and IBC Bank encountered with the development of Colorado Tower and IBC Bank Plaza.

Although Colorado Tower isn't finished, it is more than 95 percent preleased. IBC Bank Plaza is largely completed and tenants are now having their spaces built out. It also is more than 95 percent leased.